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trezor-firmware/crypto/zkp_context.c

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/**
* Copyright (c) SatoshiLabs
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
* OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
#include <assert.h>
#include <stdatomic.h>
#include <stdbool.h>
#include "memzero.h"
#include "rand.h"
#include "zkp_context.h"
#include "vendor/secp256k1-zkp/include/secp256k1.h"
static uint8_t context_buffer[SECP256K1_CONTEXT_SIZE];
static secp256k1_context *context;
static volatile atomic_flag locked;
// returns 0 on success
int secp256k1_context_writable_randomize(secp256k1_context *context_writable) {
uint8_t seed[32] = {0};
random_buffer(seed, sizeof(seed));
int returned = secp256k1_context_randomize(context_writable, seed);
memzero(seed, sizeof(seed));
if (returned != 1) {
return 1;
}
return 0;
}
bool zkp_context_is_initialized(void) { return context != NULL; }
// returns 0 on success
int zkp_context_init(void) {
assert(context == NULL);
const unsigned int context_flags =
SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY;
const size_t context_size =
secp256k1_context_preallocated_size(context_flags);
// Assert the context is as small as possible
assert(context_size == SECP256K1_CONTEXT_SIZE);
if (context_size == 0 || context_size > SECP256K1_CONTEXT_SIZE) {
return 1;
}
context =
secp256k1_context_preallocated_create(context_buffer, context_flags);
if (context == NULL) {
return 1;
}
if (secp256k1_context_writable_randomize(context) != 0) {
zkp_context_destroy();
return 1;
}
atomic_flag_clear(&locked);
return 0;
}
void zkp_context_destroy(void) {
assert(context != NULL);
secp256k1_context_preallocated_destroy(context);
memzero(context_buffer, sizeof(context_buffer));
atomic_flag_clear(&locked);
context = NULL;
}
const secp256k1_context *zkp_context_get_read_only(void) {
assert(context != NULL);
return context;
}
// returns NULL if context cannot be acquired
secp256k1_context *zkp_context_acquire_writable(void) {
assert(context != NULL);
// We don't expect the context to be used by multiple threads
if (atomic_flag_test_and_set(&locked)) {
return NULL;
}
return context;
}
void zkp_context_release_writable(void) {
assert(context != NULL);
atomic_flag_clear(&locked);
}